The present invention relates to devices for flexing metal strips and, more particularly, devices for tension leveling metal strips by bending the strips around rolls having a relatively small diameter.
In the manufacture of strip coils of common metals such as alloy steels, aluminum and the like, there exists the problem of producing a strip which is sufficiently flat to be used in end-products such as automobiles and metal furniture. In this context, the term "flat" means that, when unstressed, a section of the metallic strip is substantially planar in shape, with minimum deviations in the form of wavy edges or ripples in interior portions.
Even the most sophisticated rolling mills are unable to produce strip coils in which the strip has been reduced in thickness with sufficient uniformity to lie flat in a plane. For example, should a rolling mill reduce the thickness of a strip a larger amount along its edges than in its interior portion, thereby elongating the edges a greater amount than the interior, the resultant strip will have waves along its edges. Conversely, if the reduction in thickness of a strip is greater in its center, the center is elongated more than the edges, and a strip having a series of bubbles or buckles in its center is formed. In both cases, the deviation from flatness results from a nonuniform elongation in a metal strip caused by a nonuniform reduction in the strip thickness by the rolling mill.
In order to eliminate such defects in strip coils, the coils are processed on tension leveling lines subsequent to rolling. A typical tension leveling line, such as that disclosed in the Withrow U.S. Pat. No. 3,828,599 and the Kawaguchi et al. U.S. Pat. No. 3,958,439, includes an entry drag bridle, an exit tension bridle and flexing means positioned between the entry and exit bridles. The strip is uncoiled by an uncoiling apparatus, passed through the tension leveling line, then recoiled on a recoiler.
The flexing means typically includes a plurality of work rolls having a relatively small diameter about which the strip of material is passed. The rolls are positioned to extend transversely of the strip and are located so that the strip forms an undulating or zig-zag path as it passes from one work roll to the next. The entry drag bridle and exit tension bridle apply a tensile force to the strip as it passes through the flexing means, forcing the strip to conform to the small radiuses of the work rolls. As the strip passes about a work roll, it is deformed to provide a slight elongation of those portions across the width of the strip which are slightly shorter in length and are the cause of the deviation of the strip from the flat condition. Generally, tension leveling systems are capable of elongations of up to 2%, but most defects can be corrected by less than 1.0% elongation.
In order to provide sufficient elongation to eliminate defects in strip coils, early tension leveling systems employed a relatively large number of work rolls-on the order of six or more. It was discovered that, by reducing the diameter of the work rolls, the bending of the strip at each work roll, and its resulting elongation, was increased, thereby reducing the number of work rolls required to effect a given elongation. However, one problem in providing work rolls of a sufficiently small diameter was that the forces exerted by the moving, tensioned strip coil upon the work roll tended to deflect or bow the work roll and reduce its effectiveness.
In order to prevent the deflection of such small diameter work rolls, support rolls having a relatively large diameter were positioned on a side of the work rolls opposite the strip to reinforce the work rolls and prevent them from deflecting. For example, the Polakawski U.S. Pat. No. 3,260,093 shows a tension leveling apparatus in which a large diameter support roll is rotatably mounted on a frame and a work roll is similarly rotatably mounted on the same support frame directly above the support roll. In the Polakowski U.S. Pat. No. 3,513,677, a tension leveling device is shown in which a work roll having a relatively small diameter is cradled between two larger support rolls. The work roll and both support rolls are rotatably attached to a frame.
A problem inherent in the devices of the aforementioned Polakowski patents is that each of the work rolls is supported by two or more heavier and larger rolls. This geometry must satisfy the need to confine the work roll and support the strip tension. Consequently, work rolls cannot be selected with full freedom to meet the needs of the work material.
Another type of tension leveling system is shown in the Miyamatsu et al. U.S. Pat. No. 3,812,701. That patent shows a tension leveling system in which work rolls of a relatively small diameter are supported within a semi-cylindrical recess formed in a support and float on a liquid lubricating medium.
A problem inherent in the Miyamatsu device is that the fluid supporting the work roll must be supplied in high volume and will inevitably collect on the work material, necessitating additional time and equipment to effect subsequent removal of the fluid.
Accordingly, there is a need for a tension leveling system in which work rolls of a relatively small diameter are supported by relatively large diameter support rolls with a minimum of friction. Furthermore, such a device should be relatively simple in construction in order to keep its size and manufacturing costs to a minimum, and should be rugged and capable of withstanding the hostile environment of a steel or rolling mill.